Magnetic recording medium and method of fabricating the same

ABSTRACT

A magnetic recording has very low warp characteristics but excellent film characteristics. Particularly, the recording medium has a high coercivity with a small range of coercivity distribution, with a warp characteristic below 3 μm per radial inch. The medium is formed by heating a substrate at a high temperature with a temperature distribution on the substrate that is improved by the use of a heat distribution mask, which reduces the temperature distribution of the substrate to below ±3%.

This is a continuation application of U.S. Ser. No. 483,981, filed Jun.7, 1995 now U.S. Pat. No. 5,707,706.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to a magnetic recording medium and amethod of fabricating the same and, more particularly, to a magneticrecording medium formed by a method of heating a substrate when forminga magnetic film thereon. The present invention also relates to ahigh-quality magnetic disk capable of high-density recording, and amagnetic disk unit for using the magnetic disk.

2. Description of the Related Art

Intensive efforts have advanced in recent years in the field of magneticdisk units to increase recording density for disks of various diameters.Important factors in the increase of recording density are theimprovement of coercive force, reduction of noise attributable to therecording medium, and reduction of flying height of the magnetic headrelative to the medium. There is a correlation between coercive forceand the temperature at which the substrate is heated during theformation of the magnetic recording medium. Particularly, when thesubstrate is heated at a high temperature, the coercive force is high.

However, when the substrate is heated at a high temperature, it issubject to warping, which makes it difficult to achieve a high coerciveforce for the resulting recording medium. In fact, if the substratewarps greatly, undulations are superposed on the output waveform duringplayback, or, in extreme circumstances, the head may crash against thesubstrate as a result of the warp. Consequently, it is difficult toreduce the flying height.

Additionally, it is important that the magnetic disk have a uniformin-plane characteristic for high-density magnetic recording.

When fabricating a magnetic disk, a substrate is heated in a vacuum andthin films, including a magnetic film and a protective film, are formedon the substrate by a sputtering process (most often used to produce arigid, or hard disk) or an evaporation process (most often used forcreating a floppy disk). The properties of the magnetic thin film aregreatly dependent on the temperature of the substrate during the filmforming process. Thus, to form a thin film having a uniform quality, itis desirable to heat the substrate so that the distribution oftemperature on the substrate surface is uniform. If the substrate isheated irregularly at a high rate, the substrate may warp or crack,potentially causing the substrate to fall off its support in the vacuumvessel; at least, the substrate will be defective.

Japanese Patent Laid-Open Nos. 2-43360; 2-179879; 3-6367; and 5-144557disclose methods of regulating substrate temperature distribution.Laid-Open Nos. '360 and '367 use a sectional heater, while Laid-OpenNos. '879 and '557 disclose a heating plate between a heater and thesubstrate to heat the substrate uniformly. Japanese Patent Laid-Open No.5-33128 discloses a moving heater for heating a glass substrateuniformly.

Methods using a fixed heater have suffered from ineffective heatdistribution, which worsens as the interval between the substrate andthe heater increases. Consequently, film properties, such as coercivity,vary over the surface of the substrate. Moreover, if the heatdistribution on the substrate varies greatly, which is more likely if ahigh rate of heating is employed, the substrate warps. Further, if thesubstrate is composed of a material having a low heat conductivity, suchas glass, the substrate may crack if the range of heat distribution islarge.

Another disadvantage of the method disclosed in JP '360 is that asectional heater requires a plurality of external controllers and acomplicated heating process. JP '128 suffers from the furtherdisadvantage that a heater-moving mechanism is required which has alarge heating chamber and a complicated construction.

Currently, substrates heated by conventional methods during theformation of magnetic disks result in magnetic disks having a coerciveforce in the range of about 1500 to about 1600 Oe. Such magnetic disksare unsuitable for the high-density recording to be achieved with futuretechnology.

SUMMARY OF THE INVENTION

According to the teachings of the present invention, a magneticrecording medium is produced which has low warp characteristics, butexcellent film characteristics. Particularly, the recording medium ofthe present invention has a high coercivity with a small range ofcoercivity distribution. The improved magnetic recording medium can beproduced by heating the substrate at a high temperature with an improvedtemperature distribution, so that the tendency of the substrate to warpor crack is greatly reduced.

A uniform magnetic film and a uniform protective film can be formed onthe substrate while the substrate is being heated. Consequently, a highcoercive force of 2000 Oe (i.e., a magnetic recording medium capable ofrecording data with a density of 600 Mb/in²) or above can be achieved,and the magnetic disk has excellent in-plane film characteristics(in-plane coercive force distribution of ±5% or below). Furthermore, themagnetic disk is warped relative to its center by no more than 3 μm perinch, measured radially. For example, for a 3.5 inch magnetic disk, theperipheral part of the disk is warped no more than 10 μm with respect tothe center.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a schematic view of a sputtering-type film-forming apparatusconstructed and operating according to the teachings of the presentinvention;

FIGS. 2(a) and 2(b) are plan views of two masks employed according topreferred embodiments of the invention;

FIGS. 3(a) and 3(b) show the in-plane temperature distributions ondisk-shaped substrates according to the present invention when no maskis used and when the mask of FIG. 2(a) is used, respectively;

FIGS. 4(a) and 4(b) show in-plane temperature distributions on aNi--P/Al/Mg substrate and a glass substrate, respectively, when the maskof FIG. 2(b) is used;

FIG. 5 is a graph showing the dependence of substrate warp on heatingtemperature;

FIG. 6 schematically shows the position of a magnetic head with respectto a disk-shaped substrate;

FIG. 7 is a graph showing the relation between a flying height of themagnetic head and the warp of the disk-shaped substrate;

FIG. 8 is a fragmentary schematic sectional view of a magnetic disk;

FIG. 9 is a graph showing the relationship between coercive forcevariation and substrate heating temperature;

FIG. 10 is a graph of in-plane distribution of coercive force versuscircumferential angle for a magnetic disk employing a glass substrate;

FIG. 11 is a schematic view of a heating device for heating adisk-shaped substrate; and

FIG. 12 is a partially cut-away schematic perspective view of a magneticdisk unit.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

During a process for fabricating a magnetic recording medium, asubstrate, on which a magnetic film is formed, is heated to raise thetemperature of the substrate prior to forming the magnetic film. Tosolve a problem of temperature distribution, a mask is preferablydisposed between the heater and the substrate to control thedistribution of the heat that reaches the substrate. In particular,because the central part of the substrate is likely to be heated to atemperature that is higher than that of the peripheral part of thesubstrate, the mask preferably has a central portion corresponding tothe central portion of the substrate that absorbs or reflects part ofthe heat radiated to that portion by the heater, and a heat-transmissivepart around the central absorbing or reflecting part. Thus, the quantityof heat radiated by the heater reaches the substrate in a controlledfashion so that the temperature distribution on the substrate isuniform. This prevents the warping and cracking of the substrate thathas been a problem prior to this invention.

Preferably, the substrate is heated so that the range of in-planetemperature distribution on the substrate is ±3% or below. When thesubstrate is a 3.5 inch-diameter disk, it is preferred that the warp ofa peripheral part of the disk relative to its center be 10 μm or below.In general, however, it is preferred that the substrate have a warpcharacteristic that is no greater than 3 μm/inch, measured radially.

Since the substrate is heated to a high temperature, the mask is alsoheated to a high temperature. To prevent the mask from becoming too hot,it is preferably cooled during the heating process. For example, acooling medium may be circulated through a cooling device arranged tocool the mask. Further, the side of the mask that faces the heater maybe mirror-finished so that the surface reflects a substantial portion ofthe heat, to maintain a relatively cool temperature for the mask.

A magnetic disk unit suitable for driving a magnetic disk producedaccording to the teachings of the present invention rotatably supportsthe disk, and records or reproduces data on or from the disk by moving amagnetic head, which is preferably disposed with a flying height of 40nm or less between the head and the magnetic disk.

FIG. 1 schematically shows a single-wafer sputtering-type film-formingapparatus constructed and operating according to the teachings of thepresent invention. The film-forming apparatus has a load-lock chamber 1,a heating chamber 2, a substrate temperature monitoring chamber 3, abase film-forming chamber 4, a magnetic film-forming chamber 5, aprotective film-forming chamber 6, and an unload-lock chamber 7. Asubstrate 10, which is preferably a disk-shaped substrate to befabricated into a magnetic disk for a hard disk drive, is transferredsequentially through these processing chambers from left to right in thefigure, to form laminated layers of different thin films on thesubstrate, to complete the magnetic disk.

A substrate holder 11 supports the substrate 10 in the load-lock chamber1, and is transferred from the load-lock chamber 1 to the heatingchamber 2 after evacuating the load-lock chamber 1. The heating chamber2 preferably has a pair of heaters 8 to heat the substrate 10 on bothsides, although other arrangements for the heaters themselves may beemployed. Masks 9 are disposed between the heaters 8 and the substrate10. The masks have a special structure which will be described later.

Then, the substrate 10 is transferred to the substrate temperaturemonitoring chamber 3 and the temperature of the substrate 10 is measuredwith an infrared radiation pyrometer 12. Then, the substrate 10 istransferred to the base film forming chamber 4, where a base film 18(FIG. 18) is formed on the substrate 10 by using Cr targets 13 of purity3N. Then, the substrate 10 is transferred to the magnetic film formingchamber 5, where a magnetic film 19 is formed by using alloy targets 14of Co--Cr--Pt (18 at % Cr, 10 at % Pt). Then, the substrate 10 istransferred to the protective film forming chamber 6, where a protectivefilm 20 is formed by using C targets 15 of purity 5N. Then, thesubstrate 10 is transferred to the unload-lock chamber 7, theunload-lock chamber 7 is opened into the atmosphere, and then alubricating film 21 is formed over the protective film 20 to complete amagnetic disk as shown in FIG. 8.

As shown I FIG. 8, the disk-shaped substrate 10 is, for example, aNi--P/Al/Mg substrate, and the base film 18 of 750 Å in thickness, theCo--Cr--Ta magnetic film 19 of 350 Å in thickness, the protective film20 of 200 Å in thickness and the lubricating film of a fluorolubricantof 50 Å in thickness are formed on the substrate 10. The disk-shapedsubstrate 10 may be a glass substrate and the respective thicknesses andthe materials of the thin films formed on the disk-shaped substrate 10need not be limited to those mentioned above.

The structure of the masks 9 will be described hereinafter withreference to FIGS. 2(a) and 2(b). It was found through examination thata principal cause of cracking and warping of the substrates of magneticdisks is the abnormal heating of the central part of the substrate 10relative to the heating of the peripheral part of the same.

In general, a mask employed in the present invention is interposedbetween the heater and the substrate at a given distance from theheater. As a result, heat is distributed on the substrate in a desired,preferably fixed, distribution. Therefore, the objective uniformtemperature distribution can be achieved, reducing if not preventing thecracking of the substrate and limiting the warp to an acceptable range.These characteristics further contribute to the superior magneticcharacteristics enjoyed by the inventive recording medium.

A first embodiment employs a mask 9 of a structure as shown in FIG.2(a), which will be called a type A mask. This mask 9 has a central heatradiation screening part 9a and a heat radiation transmissive part 9baround the heat radiation screening part 91, and is formed of copper.

A second embodiment employs a mask 9 as shown in FIG. 2(b), which willbe called a type B mask. This mask 9 has a central heat radiationscreening part 9a and four heat radiation transmissive parts 9b, and isformed of copper.

FIG. 12 shows the configuration of a magnetic disk unit. A plurality ofmagnetic disks fabricated by the present invention is loaded into themagnetic disk unit to achieve high-density recording. The plurality ofmagnetic disks 30 are fixed to a spindle which is driven for spinning bya motor, not shown. A magnetic head 31 is disposed opposite to thesurface of each magnetic disk 30. The magnetic head 31 is fixed to oneend of an arm 32 and the other end of the arm 32 is attached to anactuator 33 so that the arm 32 is turned about an axis. A voice coilmotor 34 is attached to the rear end. When a current is supplied to thevoice coil motor 34, the actuator 33 is driven for turning about theaxis to position the magnetic head at a position corresponding to adesired track for recording/reproducing.

The present invention has been made on the basis of interests in thecoercive force and the characteristics of the films of a magnetic disk,and the space between the magnetic disk and the magnetic head.Characteristically, a magnetic disk provided with a magnetic film havinga coercive force of 2000 Oe or above and a range of in-plane coercivedistribution of ±5% or below is used. The magnetic head is supported forrecording/reproducing so that the space between the magnetic head andthe magnetic disk is 40 nm or below to achieve high-density recording.If the warp of the magnetic disk is 3 μm/inch along the radial directionor below relative to the central part, for example, if the warp of a 3.5inch magnetic disk is 10 μm or below, the magnetic disk is loaded intothe magnetic disk unit.

Results of experimental fabrication of magnetic disks in whichdisk-shaped substrates 10 were heated under different conditions will bedescribed hereinafter.

EXAMPLE 1

A disk-shaped substrate 10 was placed in the load-lock chamber 1 of thesputtering type film forming apparatus shown in FIG. 1, the load-lockchamber was evacuated, the disk-shaped substrate 10 was transferred tothe heating chamber 2, and then the disk-shaped substrate 10 was heatedon its both sides through the masks 9 by the heaters 8. The disk-shapedsubstrate 10 was an Al--Mg substrate of 3.5 inches in diameter and 0.8mm in thickness, provided with a plated Ni--P layer (hereinafterreferred to as "Ni--P/Al/Mg substrate") produced by Nippon Light MetalCo., Ltd. The masks 9 were the type A masks shown in FIG. 2(a).

The disk-shaped substrate 10 was heated at a heating rate of 60° C./secto 250° C. Three seconds after heating, the surface temperature of thesubstrate 10 was measured in the substrate temperature monitoringchamber 3. The temperature of the substrate 10 during heating wasmeasured with a thermocouple and temperature calibration was performed.The temperature of the substrate was measured with the infraredradiation pyrometer after determining the emissivity of the substrate.FIG. 3(b) shows the in-plane distribution of temperature thus measuredon the disk-shaped substrate 10. FIG. 3(a) shows, for comparison, thein-plane distribution of temperature on the disk-shaped substrate heatedwithout using the masks. As is obvious from the comparative observationof FIGS. 3(a) and 3(b), the uniformity of temperature gradients in thevertical direction, the horizontal direction and the radial direction isimproved when the masks 9 are disposed in front of the heaters 8.

EXAMPLE 2

Sample disk-shaped substrates 10 were a Ni--P/Al/Mg substrate and aglass substrate produced by Corning Inc. The sample disks 10 were heatedthrough the type B masks shown in FIG. 2(b) in the same manner as thatin which the sample disk 10 in the Example 1 was heated.

The Ni--P/Al/Mg substrate was heated at a heating rate of 60° C./sec to250° C. The glass substrate was heated at a heating rate of 40° C./secto 225° C. Three seconds after heating the substrates, the surfacetemperature of the substrates were measured. FIGS. 4(a) and 4(b) showtemperature distributions respectively on the Ni--P/Al/Mg substrate andthe glass substrate. The in-plane temperature differences of thedisk-shaped substrates were as small as ±3% or below.

The Ni--P/Al/Mg substrates and the glass substrates were heated at theaforesaid heating rates, respectively, to temperatures in the range of150 to 280° C. in a heating mode using the masks and in a heating modenot using any masks, and then the warps of the substrates 10 weremeasured by a substrate flatness tester of an interference system (FujiPhoto Optical Co., Ltd.). The warp of each substrate was represented bythe maximum difference between the inner circumference and the outercircumference with respect to a radial direction relative to a flatplane.

FIG. 5 shows measured warps of the disk-shaped substrates. When thesubstrate is heated to a temperature not lower than 190° C. withoutusing any mask, the warps of the substrates were 10 μm/3.5 inches orabove. When the disk-shaped substrate has such a large warp, thedisk-shaped substrate has poor film characteristics and the in-planecoercive force distribution is irregular, and it is undesirable to usesuch a disk-shaped substrate on a magnetic disk unit, and thedisk-shaped substrate is unsuitable for high-density recording.

The warps of both the Ni--P/Al/Mg substrate and the glass substrate were7 μm/3.5 inches or below when those substrates were heated through themasks 9. It is considered that the warps of the disk-shaped substratescould be reduced significantly because the disk-shaped substrates couldbe uniformly heated as shown in FIGS. 4(a) and 4(b).

EXAMPLE 3

Ni--P/Al/Mg substrates as disk-shaped substrates 10 were heated totemperatures in the range of 150 to 280° C. without using the masks bythe same method as that used in Example 1, and then the warps of thesubstrates were measured.

As shown in FIG. 6, the flying height of a head 16 at which thedisk-shaped substrate 10 starts coming into contact with the head 6 wasmeasured at different spindle speeds by an acoustic emission sensor (AEsensor) 17. Measured results are shown in FIG. 7. As is evident fromFIG. 7, the flying height of the head cannot be reduced below 40 nmunless the warp of the substrate, i.e., the warp of the peripheral partof the disk relative to the central part of the same, is 10 μm/3.5inches or less. Measured results shown in FIG. 7 show that it ispreferably for high-density recording that the warp of the peripheralpart of a 3.5 inch magnetic disk having a coercive force of 2000 Oerelative to the central part of the same is 10 μm or below and theflying height of the magnetic head, i.e., the distance between themagnetic head and the magnetic disk, is 40 nm or below. The magneticdisk unit is constructed so as to meet those conditions.

EXAMPLE 4

Ni--P/Al/Mg substrates 10 were heated to temperatures between 150 and280° C. by the method used in Example 2 using the type B masks shown inFIG. 2(b). Then, a 750 Å-thick base film 18, a 350 Å-thick magnetic film19 (Co--Cr--Ta), a 200 Å-thick protective film 20, and a 50 Å-thickfluorolubricant film were formed on each substrate 10 to fabricatemagnetic disks, as shown in FIG. 8. The base films, the magnetic films,and the protective films were formed at deposition rates of 200 Å/sec,60 Å/sec and 40 Å/sec, respectively.

Magnetic characteristics of the disks at a radius R=30 mm were measuredat different temperatures by a vibrating sample magnetometer (BHV-50,Riken Denshi), in which a circumferential magnetic field of 5000 Oe wasapplied to the magnetic disks. FIG. 9 shows the dependence of thecoercive force on the substrate heating temperature. Magnetic diskshaving substrates heated without using a mask had warp characteristicsof 10 μm for a 3.5 inch disk, and a coercive force of 1600 Oe when thesubstrate heating temperature was 190° C. or above. These magnetic diskshave poor film characteristics and are unsuitable for high-densityrecording.

Magnetic disks having substrates heated at 280° C. using the masksshowed a warp characteristic of 6.2 μm/3.5 inches, and a circumferentialcoercive force of 2100 Oe. These magnetic disks have satisfactory filmcharacteristics and are quite suitable for high-density recording.

A 3.5 inch glass substrate 10 (Corning) was heated at 250° C. using thetype B mask, and a magnetic disk was fabricated by sequentially forminga 1000 Å-thick base film 18, a 300 Å-thick magnetic film 19(Co--Cr--Pt), a 300 Å-thick protective film 20, and a 50 Å-thickfluorolubricant film, on the glass substrate 10.

The magnetic characteristics of portions of the magnetic disk on circlesof radii R=15, 20, 25, 30, 35, 40 and 45 mm at angular intervals of 3020 were measured in a circumferential magnetic field by an apparatus(RO-3000, Hitachi DECO) using the Kerr effect.

FIG. 10 shows the distribution of the in-plane coercive force of themagnetic disk. As shown, the range of radial distribution of thein-plane coercive force is 2830 to 2940 Oe, and the range ofcircumferential distribution of the in-plane coercive force on, forexample, a track of radius R=45 mm is 2830 to 2870 Oe. Therefore, therange of distribution of the in-plane coercive force in an effectiverecording region (i.e., a data guarantee region) is ±5% or below. Thewarp of the substrate is 4.7 μm/3.5 inches. The magnetic disk hassatisfactory film characteristics and is suitable for high-densityrecording.

EXAMPLE 5

As shown in FIG. 11, the type B masks 9 placed in the heating chamber 2of the sputtering-type film-forming apparatus of FIG. 1 were cooledpositively by cooling devices 23. Pure water as a cooling medium wascirculated in the direction of the arrows. The heaters 8, having heatinglamps 22, were used.

A Ni--P/Al/Mg substrate 10 was heated at 250° C. by the heaters 8 usingthe same method as in Example 1. The cooling devices 27 reduced thetemperature of the masks from 430° C. to 280° C. Thus, problemsattributable to high temperature, such as thermal deformation of themasks 9, can be prevented even when large heating power is necessary, byemploying the cooling devices 17. Since the masks 9 can be disposedclose to the heaters 8, the masks 9 can be used even if only a narrowspace exists between each heater 8 and the substrate 10.

The present invention has been described with regard to preferredembodiments. However, upon reading the foregoing disclosure, the personof ordinary skill will readily recognize various modifications that maybe made to the preferred embodiments.

For example, the surface of the heat radiation screening part 9a of themask 9 on the heater side may be mirror-finished to reflect radiationfrom the heater. In a particular example, a Ni--P/Al/Mg substrate washeated at 250° C. using the masks 9 having the mirror-finished screeningpart 9a. The temperature of the masks 9 were reduced from 430° C. to380° C. as a result of the mirror finish.

Moreover, heating efficiency can be improved by disposing reflectors orthe like behind the heaters.

The masks 9 used in the foregoing embodiments are preferably formed ofcopper having excellent heat resistance. Since the heat conductivity ofhot copper is as high as 395 J/m.s.K, the copper masks 9 can beefficiently cooled. Alternatively, the masks 9 may be formed oftitanium, a ceramic, or the like.

Further, the same heating device can be used for uniformly heatingdisk-shaped substrates of different sizes, simply by using appropriatemasks having sizes corresponding to those of the disk-shaped substrates,without requiring complex changes such as changing the distance betweenthe disk-shaped substrates and the heaters, the division of the heaters,and the change of control balance. For example, in the embodiments shownin FIGS. 2(a) and 2(b), the central screening portion 9(a) preferablyhas a diameter of about 30 mm, while the spokes of FIG. 2(a) are eachapproximately 75 mm long for each of the four spokes. In FIG. 2(b), thediameter of the transmitting circle (i.e., the end point to end pointdimension of two parallel spokes connecting at the center mask area 9a)is preferably about the diameter of the disk substrate being heated(roughly 100 mm for a 3.5 inch disk).

Additionally, the present invention is applicable to purposes other thanheating substrates to be used for forming magnetic disks. For example,the present invention enables a vacuum evaporation system to form auniform thin film on a substrate in a vacuum.

We claim:
 1. A magnetic recording disk, comprising:a substrate; a base layer on the substrate; on the base layer, a magnetic layer having a coercive force of at least 2000 Oe and a range of in-plane coercive force distribution of ±5% from innermost to outermost tracks of the magnetic layer; a protective layer on the magnetic layer; and a lubricating layer on the protective layer; wherein the substrate is warped radially from a center thereof by no more than 3 μm/inch.
 2. A magnetic recording disk as claimed in claim 1, wherein the substrate has a diameter of 1.8 inches.
 3. A magnetic recording disk as claimed in claim 1, wherein the substrate has a diameter of 2.5 inches.
 4. A magnetic recording disk as claimed in claim 1, wherein the substrate has a diameter of 3.5 inches.
 5. A magnetic recording disk as claimed in claim 1, wherein the substrate has a diameter of 5.25 inches.
 6. A magnetic recording disk as claimed in claim 1, wherein the substrate is glass.
 7. A magnetic recording disk as claimed in claim 1, wherein no part of the substrate periphery is warped relative to the substrate center by more than 10 μm.
 8. A magnetic recording disk as claimed in claim 1, wherein the substrate is Ni--P/Al--Mg.
 9. A magnetic recording disk as claimed in claim 1, wherein the substrate is at a temperature of at least 250° C., at a temperature distribution of ±3%, when the magnetic layer is formed thereon.
 10. A magnetic recording disk as claimed in claim 9, wherein the substrate has a diameter of 1.8 inches.
 11. A magnetic recording disk as claimed in claim 9, wherein the substrate has a diameter of 2.5 inches.
 12. A magnetic recording disk as claimed in claim 9, wherein the substrate has a diameter of 3.5 inches.
 13. A magnetic recording disk as claimed in claim 9, wherein the substrate has a diameter of 5.25 inches.
 14. A magnetic recording disk as claimed in claim 9, wherein the substrate is glass.
 15. A magnetic recording disk as claimed in claim 9, wherein no part of the substrate periphery is warped relative to the substrate center by more than 10 μm.
 16. A magnetic recording disk as claimed in claim 9, wherein the substrate is Ni--P/Al--Mg.
 17. A magnetic recording disk as claimed in claim 9, wherein the magnetic layer is CoCrTa.
 18. A magnetic recording disk as claimed in claim 1, wherein the magnetic layer is CoCrTa.
 19. A magnetic recording disk as claimed in claim 6, wherein the magnetic layer is CoCrTa.
 20. A magnetic recording disk as claimed in claim 8, wherein the magnetic layer is CoCrTa.
 21. A magnetic recording disk as claimed in claim 14, wherein the magnetic layer is CoCrTa.
 22. A magnetic recording disk as claimed in claim 16, wherein the magnetic layer is CoCrTa.
 23. A magnetic recording disk as claimed in claim 1, wherein the magnetic layer is CoCrPt.
 24. A magnetic recording disk as claimed in claim 6, wherein the magnetic layer is CoCrPt.
 25. A magnetic recording disk as claimed in claim 8, wherein the magnetic layer is CoCrPt.
 26. A magnetic recording disk as claimed in claim 9, wherein the magnetic layer is CoCrPt.
 27. A magnetic recording disk as claimed in claim 14, wherein the magnetic layer is CoCrPt.
 28. A magnetic recording disk as claimed in claim 16, wherein the magnetic layer is CoCrPt.
 29. A magnetic recording disk as claimed in claim 1, wherein the magnetic layer contains at least Co and Cr.
 30. A magnetic recording disk as claimed in claim 6, wherein the magnetic layer contains at least Co and Cr.
 31. A magnetic recording disk as claimed in claim 8, wherein the magnetic layer contains at least Co and Cr.
 32. A magnetic recording disk as claimed in claim 9, wherein the magnetic layer contains at least Co and Cr.
 33. A magnetic recording disk as claimed in claim 14, wherein the magnetic layer contains at least Co and Cr.
 34. A magnetic recording disk as claimed in claim 16, wherein the magnetic layer contains at least Co and Cr. 